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C-Mount "Calibrated for Bolex"


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#1 Trevor Greenfield

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Posted 18 March 2006 - 12:49 PM

Hi gents. I just bought an old 16mm non reflex camera that takes c-mount lenses with doglegs. All the time I read on Angenieux and Som Berthiot zooms, "Calibrated for Bolex" Does this have a specific meaning that in particular it won't work with another camera? Is this calibration from the rear element to the film plane or is it something else? Thanks for your help.
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#2 Jan Weis

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Posted 19 March 2006 - 04:18 AM

If the lens is c-mount it works on any c-mount camera.
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#3 santo

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Posted 19 March 2006 - 10:23 AM

Hi gents. I just bought an old 16mm non reflex camera that takes c-mount lenses with doglegs. All the time I read on Angenieux and Som Berthiot zooms, "Calibrated for Bolex" Does this have a specific meaning that in particular it won't work with another camera? Is this calibration from the rear element to the film plane or is it something else? Thanks for your help.


They are no doubt refering to the RX Bolexes, which have a beamsplitting prism which requires a different back focus adjustment compared to other c-mount cameras like Eclairs or Filmos and whatnot.

However, c-mounts do indeed require an adjustment if they are not factory original (and therefore adjusted to the camera at the factory) so that they can focus to infinity and the lens distance markings will be correct. Lenses can always be brought into focus below the infinity mark in reflex cameras using the viewfinder, but that doesn't mean the lens is set up correctly and the lens marking will be right. But it still will be very usable. Occasionally you may get lucky and a non-factory original lens will focus to infinity.

You'll never know with your non-reflex Bolex until you shoot a test reel.

Don't ask me where to get these things adjusted. Others will, I'm sure.
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#4 Freya Black

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Posted 19 March 2006 - 12:15 PM

I think what Santo is reffering to is collimation, which is when the lens is matched to the body. With screw mounts especially, but also somewhat generally, lenses are made to fit a paticular body and to focus properly on that camera. A lens from another camera may not quite work right in theory. Even bolex's can vary a bit. It's to do with the distance from the back of the lens to the film plane. You can have it collimated in special places, or you can just shoot tests and try and work out how the lens you have works with the body you have. My suspicion is that you can probably get away with stuff.

However, when people say "calibrated for Bolex" I suspect they are just talking nonsense to say that it will fit a c-mount. The RX- series of lenses were specially calibrated for the reflex bolex and are special for that camera, but I honestly can't imagine that a dogleg lens would be calibrated for a reflex bolex, as it already is reflex, why would you stick a dogleg lens on it! ;)

love

Freya
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#5 Trevor Greenfield

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Posted 19 March 2006 - 12:26 PM

LOL thank you for your advice.

I guess the best way to go is to just get one of the lenses and shoot a test, starting with infinity. (Although this will end up costing as much as the lens does).

"However, when people say "calibrated for Bolex" I suspect they are just talking nonsense to say that it will fit a c-mount. The RX- series of lenses were specially calibrated for the reflex bolex and are special for that camera, but I honestly can't imagine that a dogleg lens would be calibrated for a reflex bolex, as it already is reflex, why would you stick a dogleg lens on it! "

Thats pretty much what I figured.
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#6 Marc Alucard

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Posted 19 March 2006 - 12:59 PM

There are certain models of the Som Berthiot 17-85mm dog leg lenses that are designed for Bolex H16 cameras. The issue is the orientation of the viewfinder both optically and physically. I have one that fits right on a Bolex but won't fit on a Filmo or any Auricon models. The model I have has a double 45 degree dogleg and it interferes with every camera I have tried except the Bolex. On the other cameras the viewfinder doesn't clear the operators left side of the camera.If it will fit in a different orientation on the camera body, the viewfinder frame will not line up correctly.

The lens I have is virtually new in the box with instructions specific to the Bolex H16 and it states a lens seat/plane of 17.52 mm.


Cheers,
Marc
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#7 Freya Black

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Posted 20 March 2006 - 07:11 AM

There are certain models of the Som Berthiot 17-85mm dog leg lenses that are designed for Bolex H16 cameras. The issue is the orientation of the viewfinder both optically and physically. I have one that fits right on a Bolex but won't fit on a Filmo or any Auricon models. The model I have has a double 45 degree dogleg and it interferes with every camera I have tried except the Bolex. On the other cameras the viewfinder doesn't clear the operators left side of the camera.If it will fit in a different orientation on the camera body, the viewfinder frame will not line up correctly.

The lens I have is virtually new in the box with instructions specific to the Bolex H16 and it states a lens seat/plane of 17.52 mm.
Cheers,
Marc


Ah yes! Perhaps that is what they mean!

I have seen filmo's with the normal viewfinder removed for use with a dogleg, so perhaps it will work without the filmo viewfinder, then again perhaps not!

On a similar note, I have a few c-mount lenses that will also not fit the filmo, even tho they have standard threads. The body is just too wide and the nut at the centre of the turret stops the lens from fitting. :(

love

Freya
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